Thyroid is a small gland located at the base of the neck, just above the breastbone. Thyroid nodules are solid or fluid-filled lumps that form within the thyroid gland. Most of them are benign. Thyroid cancer accounts for only a small percentage of thyroid nodules.
Small thyroid lumps are not visible to the naked eye. Some nodules are big enough to be seen. Sometimes your doctor will feel the lump when he examines your neck.
A solitary nodule, within an otherwise apparently normal gland, is of more concern than a thyroid gland with multiple nodules (multi-nodular goiter). Multi-nodular goiters are usually benign.
Thyroid nodules are more common in women. Single nodule is four times more common in women than men.
About 45 to 75 per cent of nodules are simple cysts (colloid nodules); 15 to 40 percent are benign tumours (adenomas); and only eight to 20 per cent are cancerous.
A patient with a history of radiation treatment to the neck, or any radiation exposure near the thyroid gland, has increased risk of developing nodules. These nodules tend to develop long after the radiation exposure. Family history of thyroid cancer increases the likelihood of a thyroid nodule being malignant.
How do we investigate a solitary thyroid nodule?
The most recent guideline from the American Thyroid Association recommends measurement of thyroid stimulating hormone (TSH) level in the blood and ultrasound of the neck in all patients with a thyroid nodule, says an article in the Canadian Medical Association Journal (CMAJ December 6, 2016).
Ultrasound is a good test for thyroid lumps. It can tell us if there is more than one nodule, if the lump is solid, cystic or mixed; and it is the best method to determine the size of the nodule.
Blood test is also useful. A low TSH level (< 0.3 mU/L) suggests an autonomously functioning nodule, and a thyroid scan with iodine-123 should be performed.
Although nodules are present in 20 to 70 per cent of individuals, most do not require biopsy.
If the nodule is hyper-functioning then it requires medical treatment. Surgery is rarely indicated.
If the TSH level is normal or high (> 5 mU/L), then fine-needle aspiration (FNA) biopsy should be considered. All thyroid nodules do not need a needle biopsy. Only non-cystic nodules greater than one to two cm need to be biopsied. FNA biopsy is recommended for nodules with features on ultrasound that indicate higher risk of malignant disease.
If the needle biopsy is negative for cancer in the first instance then the new guidelines recommend a repeat needle biopsy after three months. Repeat needle biopsy yields a more definitive diagnosis in up to 90 per cent of cases based on high-quality studies, says the CMAJ article.
After two benign needle biopsy results, ultrasound surveillance is no longer indicated. However, if the lump gets bigger or causes symptoms then there is an indication for surgical treatment.
So, a solitary thyroid nodule is not always malignant. But it should not be ignored. Appropriate investigations should be done to rule out cancer.
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